This invention relates generally to a thin film inductive write head for magnetic recording, and more particularly to a thin film write head having an improved write gap.
In a magnetic recording disk drive, data is written by thin film magnetic transducers called xe2x80x9cwrite headsxe2x80x9d that are supported over the surface of the disk while the disk is rotated at high speed. Each write head is located on the trailing surface of a slider that is supported by a thin cushion of air (an xe2x80x9cair bearingxe2x80x9d) produced by the disk""s high rotational speed.
A prior art thin film inductive write head is shown in the side sectional view of FIG. 1 and the partial end view, as seen from the disk, of FIG. 2. FIG. 1 also depicts the pole tips facing a magnetic recording disk that has a magnetic layer ML on the disk substrate SB and a protective overcoat OC on the ML. The distance D from the ends of the pole tips to the middle of the ML is referred to as the magnetic spacing. The write head includes a coil C located between bottom and top pole pieces P1 and P2, respectively. The pole pieces are formed from thin films (xe2x80x9clayersxe2x80x9d) of magnetic material and have a pole tip height dimension commonly called the xe2x80x9cthroat heightxe2x80x9d. The throat height is measured between an air-bearing surface (xe2x80x9cABSxe2x80x9d), formed by polishing the tips of the pole pieces, and a xe2x80x9czero throat levelxe2x80x9d, where the bottom pole piece P1 and the top pole piece P2 converge at the write gap G. A thin film inductive write head also includes a xe2x80x9cpole tip regionxe2x80x9d which is located between the ABS and the zero throat level, and a xe2x80x9cback regionxe2x80x9d which extends back from the zero throat level to and including a back gap BG. Each pole piece has a pole tip in the pole tip region and a back portion in the back region. The pole pieces are connected together at the back gap BG. The pole tips are extensions of the bottom and top pole pieces P1 and P2 of the write head. Each of the pole pieces P1 and P2 transitions to a pole tip (PT2 and PT1a, Pt1b) in the pole tip region. The pole tips are separated by a gap G, which is a thin layer of nonmagnetic material, typically sputter deposited insulating alumina (Al2O3) or plated nickel-phosphorous (NiP). During the write process, write currents are sent to the coil C and a magnetic field is generated across the write gap G. The fringing field from the write gap G is used to reverse the magnetization in the magnetic layer ML, resulting in the recording of data on the disk. The width W of the pole tip PT2 (FIG. 2) determines the width of the data track on the disk.
The write head shown in FIGS. 1 and 2 is depicted as part of a prior art xe2x80x9cmergedxe2x80x9d read/write head that employs a magnetoresistive (xe2x80x9cMRxe2x80x9d) read element and an inductive write element in combination. The MR read element is located between bottom shield S1 and top shield S2. The bottom shield S1 is formed on a substrate, typically the trailing surface of an air-bearing slider. The top shield S2 also functions as the bottom pole P1 of the write head. In the merged MR head the pole tip of pole P1 is constructed as a narrow xe2x80x9cpedestalxe2x80x9d pole tip portion PT1b on top of the second shield layer S2, as shown in FIG. 2, with the P1/S2 layer then serving as a wider bottom pole tip portion PT1a. Both of these pole tip portions PT1b and PT1a form the pole tip of the bottom pole P1, with the pole tip portion PT1b forming a pedestal on the pole tip portion PT1a. In the write head shown in FIG. 1, the throat height is less than the height of PT1b because P2 does not converge at precisely where PT1b begins but at a point closer to the ABS.
The write field contour generated by the pole tips of a thin field inductive write head has a three-dimensional shape, referred to as the write xe2x80x9cbubblexe2x80x9d. The shape of the write bubble is defined by all points in space where the field is equal to the write threshold, which is the field strength sufficient to change the magnetization in the magnetic layer of the disk, i.e., the coercivity of the magnetic layer. For a given deep-gap field at the throat region of the write head, a larger write gap results in a wider write bubble along the in-track direction to yield better overwrite performance, i.e., the ability to overcome the influence of previously written data. However, a larger write gap also results in a wider write bubble in the off-track direction to yield a wider data track, thereby decreasing the track density that can be achieved on the disk.
To improve on this fundamental tradeoff between overwrite performance versus track density, what is needed is a thin film inductive write head that can create an improved write bubble geometry with a higher in-track to off-track aspect ratio. Such an improvement is especially desirable for very high data density applications, where overwrite performance is typically severely compromised by the need for small write gaps to maintain closely-spaced and narrow data tracks.
The invention is a thin film inductive write head with a write gap formed as a lamination of alternating layers of a nonmagnetic gap layer and a ferromagnetic spacer layer. There are N gap layers and Nxe2x88x921 spacer layers, with each pole tip of the write head being located adjacent to a gap layer. The spacer layers in the gap structure are formed of a ferromagnetic material with a high saturation moment density (Bs) that is close to the BS of the spacer material from which the pole tips are formed. Unlike the pole tips, the spacer layers are not part of a magnetic circuit and are magnetically isolated, i.e., completely surrounded by nonmagnetic gap material. The effect of the spacer layers is to effectively divide the gap into a plurality of smaller gaps. The write head with the laminated gap produces a write bubble that is narrower in the off-track direction and larger in the in-track direction with track edge writing similar to that of a small gap write head.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.